Wireless telecommunications systems in the prior art typically employ a linear, high-power amplifier with each transmitting antenna at the base station. Typically, the linear amplifier is used to amplify the modulated radio frequency (RF) signals of a plurality of frequency channels for transmission to mobile or stationary users. Multi-sector systems employ a plurality of directional antennas to radiate directional beams over complementing azimuthal sectors, thereby attaining 360.degree. coverage with improved range. Single sector systems utilize a single omnidirectional antenna to provide 360.degree. coverage. In either case, as the amplifier input power increases, so can the intermodulation distortion products, which result in undesirable interchannel interference.
When the traffic on the telecommunications system is operating near its maximum capacity, the IMD products generated can become excessively high, since at this time the amplifiers are generally saturated. In directional antenna systems, a particular problem arises when a large number of users are communicating from a single location. In this scenario, the amplifier associated with the antenna transmitting to that location can become saturated, while the other amplifiers, which service other azimuthal sectors, may be underutilized. In addition to generating high IMD products, the reliability of the saturated, overburdened amplifier can decrease as thermal stress begins to take its toll.
One solution to these problems is disclosed in co-pending U.S. patent application Ser. No. 08/506,286 entitled "Power Shared Linear Amplifier Network" and assigned to the assignee herein. Therein, a system is described, which comprises a plurality of amplifiers to produce the total radiated power, with each amplifier providing an approximately equal amount of amplified RF power. This is typically accomplished by using at least one power sharing network, such as a Butler matrix, to spread the input signal among a number of output ports with a phase progression therebetween. Typically, with this system, no single amplifier will be driven deeper into saturation than will the others, thereby enhancing the amplifier reliability and reducing IMD product generation. Optionally, a second Butler matrix is used to recombine the RF power after amplification by the linear amplifiers so that the directional radiating antennas (if used) need not share the same aperture.